Engine emission control systems may utilize various exhaust sensors. One example sensor may be a particulate matter sensor which indicates particulate matter mass and/or concentration in the exhaust gas. In one example, the particulate matter sensor may operate by accumulating particulate matter over time and providing an indication of the degree of accumulation as a measure of exhaust particulate matter levels.
Particulate matter sensors may encounter problems with non-uniform deposition of soot on the sensor due to a bias in flow distribution across the surface of the sensor. Further, particulate matter sensors may be prone to contamination from an impingement of water droplets and/or larger particulates present in the exhaust gases. This contamination may lead to errors in sensor output. Furthermore, sensor regeneration may be inadequate when a substantial volume of exhaust gases stream across the particulate matter sensor.
The inventors herein have recognized the above issues and identified an approach to at least partly address the issues. In one example approach, a system for sensing particulate matter in an exhaust passage of an engine is provided. The system comprises a tube positioned in an exhaust passage of an engine, a particulate matter sensor positioned within the tube, and a flow guiding plate positioned within the tube substantially parallel to a vertical axis of the tube. The guiding plate comprises a plurality of projections with surfaces of the projections defining an interior passage in proximity to the particulate matter sensor, the surfaces of the projections directing flow against the particulate matter sensor.
As one example, a particulate matter (PM) sensor may be disposed within a tube fixed to a wall of an exhaust passage. The tube may further comprise a flow guiding plate located downstream of the PM sensor. The PM sensor may comprise an electric circuit on an upstream surface directed away from the guiding plate. The PM sensor may further comprise two separate electrodes located on a downstream surface. An interior passage (e.g., a central chamber) may be located between the PM sensor and guiding plate. A sample of exhaust gas may enter the tube via an inlet located on a bottom portion of the tube. Larger particulates and/or water droplets may flow through a drainage hole directly downstream of the inlet on the bottom portion of the tube. The sample of exhaust gas may be conducted up along an outside of the guiding plate before flowing down into the central chamber The sample of exhaust gas flows through guides of the guiding plate and may be evenly distributed across the downstream surface of the PM sensor. Finally, the sample of exhaust gas may exit the tube and flow into the exhaust passage via outlets located at an interface between the guiding plate and the tube.
In this way, a PM sensor may be exposed to a more uniform flow distribution across its surface. By flowing the sample of exhaust gas from a lower portion of the tube to a higher portion of the tube, a flow rate and/or volume of exhaust gas entering the central chamber may be controlled. Further, distribution of particulate matter from the sample of exhaust gas onto the PM sensor may be more evenly distributed due to the guiding plate, which may mix and guide exhaust flow across a total surface area of the downstream surface of the PM sensor. By providing a more even and controlled flow of the sample exhaust gas onto the downstream surface, particulate filter regeneration and/or determination of degradation of the PF in the exhaust passage may occur more accurately. Further, the PM sensor may be protected from larger particulates and water droplets, as they may flow through the drainage hole due to their greater momentum. Overall, functioning of the PM sensor may be improved and may be more reliable.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.